A drawing with nominal values only has not specified anything yet
The cover of this article is an unremarkable stackup cross-section: Solder-Stop, Cu 18µm + plating, 2x Prepreg 2116, Core 300µm alternating down the stack, with a column of thickness callouts on the right reading 35µm, 230µm, 300µm, 340µm. Along the left margin runs one small rotated note: "Only nominal values".
That note describes the actual state of most outline drawings we receive. Board length 100.00 mm, slot width 3.00 mm, cutout φ12.00 mm, thickness 1.60 mm — every number is there, and not one of them carries a tolerance. Engineering review then has to ask: is that 100.00 a critical dimension mating into an enclosure, or an outer frame with clearance? Is the 3.00 mm slot a cable pass-through or a mechanical locating slot? Does the 1.60 mm thickness have to fit a connector slot?
The underlying point is simple: a nominal value states the target, a tolerance states the acceptable range, and only an acceptable range can be manufactured and inspected against. Leaving tolerances off is not the same as "use your standard" resolving itself correctly. It hands the decision to the fabricator, who can only apply general tolerances. If one of your dimensions genuinely needs to be tighter than the general value, that requirement is permanently lost on the drawing.
So this article does not explain what profiling is as a process step, and does not discuss cutters or machine parameters. It answers one thing: how to specify tolerances for outline, slots, internal cutouts, V-cut and thickness so they land inside the windows Sunking PCB has published.
The published profiling and mechanical tolerance window
Here are the values you can cite directly. All of them are taken from the manufacturing tolerances page, which states explicitly that imperial values are authoritative and metric equivalents are provided for convenience. That distinction matters when you draw, and the reason comes later.
| Item | Tolerance |
|---|---|
| Board Outline | ±0.005″ (≈0.13 mm) |
| Slots | ±0.005″ (≈0.13 mm) |
| Internal Cutouts | Non-plated ±0.005″; plated ±0.010″ |
| Scoring (V-Cut) | Location ±0.003″; Depth ±0.005″ |
| Thickness | ±10% or ±0.005″, whichever is greater |
| Hole Size | Plated (<0.247″) ±0.003″; non-plated (<0.250″) ±0.002″; larger holes ±0.005″ |
| Hole Location (annular ring / pad size) | ±0.003″ (≈0.076 mm) |
| Soldermask Registration | ±0.003″, depth ±0.005″ |
| Trace Width / Copper-to-Copper Spacing | ±20% |
Three entries in that table deserve separate attention, because they are where outline problems usually originate.
First, outline and slots share ±0.005″, but internal cutouts split into plated and non-plated. Non-plated cutouts get ±0.005″; plated cutouts open up to ±0.010″, exactly double. The reason is not mysterious: a plated cutout edge goes through subsequent metallisation, so its final size is not fixed by one machining operation. If your cutout is a locating window for a part, design it non-plated and you get the tighter grade directly. Drawing a window that needs ±0.005″ as a plated cutout doubles your own tolerance.
Second, thickness tolerance is "±10% or ±0.005″, whichever is greater" — a conditional rule, not a fixed number. Thin boards are floored by ±0.005″ while thicker boards are driven by ±10%, and the crossover sits near 0.050″ (≈1.27 mm): below that nominal thickness ±0.005″ is the larger term, above it ±10% is. A common 1.60 mm (≈0.063″) board falls on the ±10% side. If a connector slot or enclosure channel constrains your board thickness, work the rule out yourself first, then decide whether you need to request something tighter.
Third, V-cut location and depth are two independent tolerances with different meanings. Location ±0.003″ governs where the score line sits; depth ±0.005″ governs how much material is removed. Why they are given separately is the next section.
For the overall dimensional envelope see manufacturing capabilities: maximum board size is 600×570 mm / 610×1100 mm / 1250×570 mm across the Standard / Advanced / R&D grades, minimum board size 50×50 mm / 30×30 mm / 5×5 mm, and board thickness runs from 0.6 / 0.40 / 0.20 mm up to 4 / 6 / 6 mm. Your outline has to sit inside that window before tolerances are worth discussing. A design beyond the finished-size limit is not a tolerance question, it is a splitting or re-panelling question and needs engineering review.
V-cut: the score line centre is the board edge, and that changes copper layout
The manufacturing tolerances page carries one decisive sentence about scoring: the center of the score line is the board edge; plan copper clearance accordingly.
That sentence carries far more weight than its length suggests. V-cut scores a V-groove from both faces and leaves a web of material in the middle, which is broken along that web during depanelisation. The machine follows a line, while the edge you drew is a finished contour. The page reconciles the two by defining score line centre = board edge. Consequently:
- copper-to-edge distance is measured from the score line centre, not from some "groove edge";
- the ±0.003″ location tolerance shifts that datum directly, so your copper clearance must absorb it;
- the ±0.005″ depth tolerance affects web consistency and break behaviour, not edge position, so it must not be lumped together with location.
This also explains the exception in the edge clearance rule. The page states: keep outer copper ≥0.005″ and inner copper ≥0.010″ from the board edge (except scored arrays). A routed edge and a scored edge are fundamentally different boundary conditions — routing is a contour produced by a cutter actually removing material, scoring is a pre-defined break line. The exception is not extra headroom for you; it signals that copper clearance on a scored edge needs its own review and cannot inherit the routed-edge 0.005″/0.010″ figures. Where the page publishes no specific number for scored edges, write "subject to engineering review" on the drawing rather than deriving one yourself.
While we are here: why do inner and outer differ by a factor of two (0.005″ vs 0.010″)? Inner copper is buried in the stack, and cutting the edge has to avoid delamination and inner-layer copper exposure, so a larger margin is warranted. This is a different matter from the minimum line width in manufacturing capabilities, which is 4/4, 3/3 and 2/2 mil for both inner and outer layers — line width is about etch resolution, edge clearance is about mechanical cutting and stack integrity.
Datums: tolerances only stay bounded when there is a single origin
The most common and most overlooked error on an outline drawing is not a loose tolerance. It is no defined datum.
Take one board. If length is dimensioned from the left edge to the right edge, the slot from the right edge to the slot centre, and the cutout from some hole, each of those three dimensions can be within tolerance while the assembly still does not fit — because each segment accumulates from the realised result of the previous one. Board outline ±0.005″ is tight on its own, but three chained segments no longer produce a worst case of ±0.005″.
There is only one way to avoid stacking: dimension all critical features from the same datum. Among the features available as a datum, hole position accuracy is published — hole location (annular ring / pad size) is ±0.003″, one grade tighter than the ±0.005″ outline. In practice:
- dimensions that must mate precisely with an enclosure, bracket or connector should be referenced to holes, not to a routed edge;
- plain outer-frame dimensions are fine on the outline tolerance and do not need to be tighter;
- never hang a precision-fit slot off the board edge through two or three chained dimensions.
The page also gives inner layer hole to copper as hole size + 0.020″ (≈0.51 mm), vias and component holes at ≥0.010″ (≈0.25 mm) from copper of a different net, and pads for plated holes at ≥0.010″ larger than the hole to meet the IPC-6012 annular ring. Those are the constraints to check in parallel when a hole becomes your datum — a datum hole with insufficient annular ring is not a reliable datum.
Imperial is authoritative: do not generate a third set of numbers
The manufacturing tolerances page states that imperial values are authoritative, with metric equivalents provided for convenience. That statement has direct drawing consequences.
The metric equivalent of ±0.005″ is written ≈0.13 mm. If you put ±0.13 mm on a drawing, strictly it is slightly looser than ±0.005″ (= 0.127 mm). If you put ±0.12 mm, it is slightly tighter — and that tightening is something you introduced, not something anyone committed to. Likewise ±0.003″ = 0.0762 mm; ±0.076 mm is the page's own conversion, while ±0.08 mm is a third set of numbers.
Practically: drawing in metric is entirely fine, but either cite the conversions the page gives (0.13 mm / 0.076 mm / 0.51 mm / 0.25 mm) or note on the drawing that tolerances are authoritative in imperial. Do not round your own values into existence, and do not convert metric back to imperial for comparison — after two roundings the deviation has no engineering meaning and only becomes a dispute at inspection.
Thickness deserves particular care because it is a greater-of-percentage-or-absolute composite rule. At 1.6 mm nominal: ±10% = ±0.16 mm, ±0.005″ ≈ ±0.13 mm, so the greater is ±0.16 mm. At 0.8 mm nominal: ±10% = ±0.08 mm, ±0.005″ ≈ ±0.13 mm, so the absolute term governs and the tolerance is ≈±0.13 mm. Thin boards carry a wider thickness tolerance than a percentage-only intuition suggests, which has to be worked out in advance wherever slot fit or pressed total height is involved.
Pre-release self-check for outline data
Condensed into a list you can work against. This is not a general checklist; it covers the outline and mechanical dimension only:
- Finished board size sits inside the window published in manufacturing capabilities: maximum 600×570 / 610×1100 / 1250×570 mm and minimum 50×50 / 30×30 / 5×5 mm by grade.
- Outline contour is a closed, single, non-self-intersecting path, and the drawing states which layer carries the outline.
- Every critical outline dimension carries a tolerance, or the drawing states "untoleranced dimensions per Sunking PCB standard tolerances". Do not leave bare nominal values — that is exactly the state of the cover image.
- Slots and internal cutouts are individually marked plated or non-plated. Non-plated cutouts can use ±0.005″, plated cutouts are ±0.010″, and locating windows needing a close fit should be non-plated.
- V-cut score line positions are shown, and all copper clearances are computed from the score line centre. Do not inherit routed-edge figures for scored edges; write "subject to engineering review".
- Edge copper clearance on routed edges: outer copper ≥0.005″, inner copper ≥0.010″, checked layer by layer rather than on the top layer only.
- Thickness tolerance worked out yourself under "±10% or ±0.005″, whichever is greater", with the resulting range confirmed acceptable to downstream assembly.
- A single datum, with precision-fit dimensions referenced to hole locations (±0.003″) rather than hanging off the end of a dimension chain.
- Units and rounding: metric callouts cite the page's own conversions, or the drawing notes that imperial governs. No third set of numbers.
- Anything tighter than standard listed separately, with its purpose stated (enclosure fit, slot thickness, locating window). Those requests are subject to engineering review and should not be buried among ordinary dimensions for the fabricator to discover.
Once the data is complete you can move to online quote. Inspection criteria and class conventions are on quality assurance — the page publishes IPC-A-600 Class 2/3 and 100% electrical test, so confirm the specific class at review. Surface finish affects the final condition of edges and hole walls; selection guidance is on surface finish. For how copper weight constrains minimum line width, see PCB copper thickness options and design rules. Impedance tolerance classes (±5% / ±10%) are covered separately in impedance control PCB tolerance classes — an independent set of requirements from the mechanical tolerances here.
Cover image alt
Layer stackup cross-section diagram: two vertical stack illustrations with alternating bands labelled solder-stop, Cu 18µm + plating, 2x Prepreg 2116 and Core 300µm, thickness callouts of 35µm, 230µm, 300µm and 340µm on the right-hand diagram, a rotated note reading "Only nominal values" along the left margin, and a vertical plated barrel running through the stack.
FAQ
Q: What happens if my drawing carries no outline tolerance?
A: Standard tolerance applies, which is board outline ±0.005″ (≈0.13 mm). The risk is that if one of your dimensions genuinely needs to be tighter, that requirement leaves no trace on the drawing and neither fabrication nor inspection will know about it. Either tolerance each critical dimension, or at minimum note "untoleranced dimensions per standard tolerances" and list the tighter items separately.
Q: Board outline ±0.005″ is measured from where to where?
A: It is the deviation of the finished contour from the nominal contour on the drawing. The datum is what matters: if your dimensions are chained (A to B, B to C, C to D), tolerances accumulate along the chain and the worst case is well beyond a single ±0.005″. Precision-fit dimensions should originate from one datum, preferably a hole location at ±0.003″.
Q: What is the difference between V-cut location and depth tolerance, and which affects board size?
A: Location ±0.003″ affects board size, because the score line centre is the board edge, so shifting the line shifts the edge. Depth ±0.005″ affects the remaining web and break behaviour, not edge position. They are independent items and cannot be merged into one "V-cut tolerance".
Q: Why is a plated cutout tolerance twice as wide as non-plated?
A: The page gives non-plated ±0.005″ and plated ±0.010″. A plated cutout edge is metallised after forming, so its final size is not determined by a single machining operation, and the tolerance is correspondingly wider. If the cutout serves mechanical location, design it non-plated to obtain the tighter grade.
Q: What is the actual thickness tolerance on a 1.6 mm board?
A: Under "±10% or ±0.005″, whichever is greater": ±10% = ±0.16 mm and ±0.005″ ≈ ±0.13 mm, so the greater is ±0.16 mm. At 0.8 mm, ±10% = ±0.08 mm is smaller than ±0.13 mm, so the tolerance is ≈±0.13 mm. Thin boards carry a wider thickness tolerance than a percentage-only reading suggests.
Q: How far should copper be kept from a V-cut edge?
A: The published 0.005″/0.010″ edge clearance explicitly lists scored arrays as an exception and gives no specific figure for scored edges. So routed-edge values cannot be inherited and must not be derived. Mark it "subject to engineering review" on the drawing and settle it at review. The one established premise is that the distance is measured from the score line centre.
Q: Can I request tolerances tighter than standard?
A: The manufacturing tolerances page states that "tighter tolerances may be available on request; contact us if a standard tolerance does not meet your specifications". How tight a given dimension can go depends on thickness, layer count, material and outline complexity, and is subject to engineering review. No committed figure is given here.